Beardo, if I've got this right (bear with me, I'm a bit slow on the uptake at times), you're thinking of buying a nicely-bred filly foal, with a view to keeping her to breed from? In that case, you'll be waiting around 4-5 years, with her doing no more than cost you keep until she can be bred from, unless you plan to race her in the interim - which doesn't seem to be your plan.
So, you'll have an unraced mare to offer prospective buyers of her future foals? She won't have any race history and thus won't have a smudge of black type against her name. That really only works if she's by a stallion that everyone wants, one which has not only demonstrated his skills in racing, but also in begetting winners. It is so not a good idea to send an unraced mare to an unproven (or new) sire unless she has a bloodline that's currently desirable.
Otherwise, Songsheet's given you the benefit of some 30+ years experience in breeding in a nutshell, and all I can say is, if you've got the money, then follow it. You'll also need adequate stabling and sufficient field facilities for the mare and her own foal, someone who knows how to handle mares and foals, you'll need to pay someone to prep her offspring for the foal sales, pay for transport to the sale, and pay the sale's entry fee.
Just as an example for you, I bought a 5 y.o. unraced DANETIME (not as good as DANEHILL DANCER, but still got the wanted DANEHILL genes) mare i/f to new sire MAJESTIC MISSILE. I paid £5000 for her out of Goff's sales in Naas last year. There were transportation costs from Ireland to Songsheet's farm in Somerset, there was her keep at the farm, there were the vet's fees to both the mare and subsequent colt foal, then her and the foal's additional keep, around £300 in preparation fees for the foal for the sale, transport to the sale, and a £540 sale entry fee. Altogether, I probably forked out a total of around £7000. The colt sold for the minimum bid (800 guineas) = £840 and was sold to an Irish stud, who's pinhooking him for sales later this year. I'll let you do the Maths on that, see the loss made, and that was at the very cheap end of the business.
If you looked over any of last year's sales catalogues and noted how many foals were returned home unsold, and how many didn't make either their reserves or even the minimum bid - well, I wouldn't want to put you off, but the adage about the way to make a small fortune in breeding is to start with a large one, came all too true for even the biggest, the most experienced and highly-regarded studs, as much as the small-time breeder.